It is common practice to metallize or coat various articles fashioned from such diverse materials as steel, rubber, plastic and the like by vapor depositing aluminum thereon.
In practice, the actual coating or metallizing or an article is carried out in a vacuum chamber which contains both the metal to be vaporized and, in a spaced apart relationship, the article or web to be coated or metallized. Generally, the metal to be vaporized is deposited at a controlled rate into the refractory vessel or crucible, which is at a temperature sufficient to cause the metal to become molten and commence to vaporize.
In the foregoing general process it is essential that a vessel or crucible be employed which does not react substantially with the molten metal such as aluminum. This requirement is exceptionally well satisfied by fashioning such a vessel or crucible from a refractory material such as boron nitride or a boron nitride base composite. However, one difficult which is experienced with the use of this type of material is slow or limited wetting of the boron nitride base evaporation vessel by molten metal such as aluminum during the start up of the metallizing apparatus. This delay in wetting reduces the total efficiency of the metallizing process and is to be avoided, if possible.
U.S. Pat. No. 3,724,996 discloses a boron nitride-containing vaporization vessel having deposited on its surface a zirconium-silicon alloy that is applied by reacting a portion of the zirconium-silicon alloy with the contacted boron nitride containing vessel at elevated temperatures.
U.S. Pat. No. 3,730,507 discloses a boron nitride containing vaporization vessel having deposited on its surface a titanium silicon alloy in which the coating had been formed by reacting a portion of the titanium silicon base alloy with the contacted boron nitride portion of the vessel at elevated temperatures.
In using the boron nitride containing vessels to vaporize aluminum, each vessel acts as a resistive heater, a container for the molten aluminum, and a surface for the aluminum to vaporize from. Although the prior art vessels perform well, the novel coating of this invention permits lower temperature wetting by aluminum, improved vessel life, immediate stabilization of a new boat at a uniform vaporization rate, uniform wear of the vessel, and uniform metal deposition on the web. The delay in wet-in of a vessel reduces the overall efficiency of the metallizing process. In some instances an operator could overheat the vessel to get as quick a wet-in as possible and then if he continued to run the process at this higher temperature, the life of the vessel could be shortened.
It is an object of the present invention to provide a boron nitride containing vessel with a novel coating that will enable the vessel to be used with molten metals, such as aluminum, in various vaporizing processes.
It is another object of the present invention to provide a boron nitride containing evaporation vessel with a titanium-iron-silicon base coating that is readily wetted by molten metals, such as molten aluminum.
It is another object of the present invention to provide a boron nitride containing vessel with a titanium-iron-silicon base coating that enables the vessel to be used efficiently in vaporizing aluminum for packaging, capacitor film and solar/microwave film applications.
The foregoing and additional objects will become more apparent from the description and disclosure hereinafter.